Cable tuner circuits are used to receive a television signal from a television signal provider and to tune into a single channel within the television signal in order to present audio and video information from that channel to an end user. Cable tuners that operate using a superheterodyne circuit for use in a superheterodyne method of processing television signal information are commonplace. A superheterodyne receiver converts a desired signal to an intermediate frequency (IF) for filtering using a fixed bandpass filter. Signals having been passed through the fixed bandpass filter are processed by a second primary component of the receiver. A fixed bandpass filter is preferred because the filter characteristics are more readily and precisely determinable and hence the desired signal is more readily distinguishable from noise and other unwanted signals. Surface acoustic wave (SAW) filters are exemplary of the state of the art fixed bandpass filters used in television tuners.
SAW filter, brought upon a significant change in tuner design. With the use of SAW filters, some discrete filter components such as capacitors and manually tuned inductors used within the tuner circuit were reduced in number. With the use of SAW filters, filtering performance is improved within tuners as compared to prior techniques. Additionally, through the use of SAW filters, tuners were manufactured that required less space and were somewhat less costly than their counterparts. However, the SAW filter, which is fabricated on a ceramic substrate, is an off-chip device. It is also a rather low impedance device, and thus, requires low impedance matching to its input port. Additionally with the use of SAW filters, prior signal amplification requirements result in complications such as significant amplifier power consumption. Furthermore, broadband circuits, especially amplifier circuits, tend to consume more power as compared to narrower band circuits. Consequently, as the upper frequency for receivable TV signals increases, the power consumption of broadband amplifiers increases, particularly when used in combination with SAW filters. Heat dissipation and heat concentration in the already reduced surface area of a small TV tuner adds heat stress to the circuit components therein as well as to nearby elements of the electronic apparatus. The consequent heat stress thus unfavorably affects the functional reliability of both the tuner and any nearby elements. Furthermore, when more electrical components that are used within tuner circuits, more signal delays are observed as well as signal artifacts.
A need therefore exists to provide an improved filter in cable tuner circuits that consumes less electrical power than conventional designs. It is therefore an object of the invention to provide a television tuner having filters that are integrable within a semiconductor substrate and one that lends itself to miniaturization.